This invention relates generally to temperature responsive control apparatus and more specifically to control apparatus in which an input fluid pressure signal which varies as a function of temperature is amplified and is converted to an output pressure signal or equivalent position signal for control purposes.
Typically, the input pressure signal is produced by the expansion and contraction of a gas contained within a bulb or probe which senses a variable temperature condition while the output pressure signal is produced hydraulically. When conventional temperature responsive control apparatus is used in certain applications as, for example, a fuel control for a gas turbine engine, the time delay or lag between a change in the sensed temperature and a change in the output signal is too great to enable adequate control over the rate of fuel flow to the engine.
It has been recognized that the response characteristics of the control apparatus should be as fast as possible. One scheme for decreasing the response time is disclosed in Peczkowski U.S. Pat. No. 3,322,344. In that arrangement, the gas from the probe is transmitted to a receiver and acts in one direction against a valve which controls the output pressure. A hydraulic feedback pressure of the same magnitude as the output pressure acts against the valve in the opposite direction. To improve the response characteristics, the gas from the probe passes through a restriction in the receiver and causes the input pressure signal to change values at a different rate from the rate actually produced by a change in sensed temperature.